1. Field of the Invention
The present invention relates, generally, to methods of preparing micro-structured R—Fe—B type anisotropic powders for bonded magnets having high coercivity and thus prepared magnet powders. More specifically, the present invention relates to a method of preparing a micro-structured powder for bonded magnets having high coercivity, characterized in that R—Fe—B type anisotropic sintered magnets or scraps thereof are crushed to prepare 50–500 μm sized magnet powders, which are then mixed with 1–10 wt % of rare earth fluoride (RF3) powders and thermally treated at high temperatures (500–1100° C.) in a vacuum or an inert gas, to cause the change of the matrix-near surface and grain boundary of the powders, thereby exhibiting advantages of low preparation costs by recycling magnet scraps, simplified mass production, minimal environmental contamination by such a recycling process, and the preparation of stable anisotropic powders having high coercivity. Further, a recycling process of the magnet scraps is efficiently improved, resulting in increased productivity and reliability. In addition, a micro-structured powder for bonded magnets having high coercivity prepared by the above method is provided.
2. Description of the Related Art
In general, R—Fe—B (Nd—Fe—B) type magnets developed already have high magnetic characteristics, and are employed to decrease the size of electric and electronic products. Further, the R—Fe—B type magnets have high performance and thus applications thereof become wide.
Powders for the R—Fe—B type magnets are classified into nano-structured isotropic powders using a melt spinning process, and anisotropic powders by use of an HDDR (Hydrogen Disproportionation Desorption Recombination) process.
As the above applications of the R—Fe—B type magnets, there are high-powered motor products, such as VCRs laser printers, hard disk drives, robots, electric power steering, automobile fuel pumps, washing machines, refrigerators, and air conditioners, speakers, buzzers, sensors, and magnetic gears. As well, the above magnet can function to realize small sizes and energy-saving of end products, and thus applied for digital cameras, camcorders, office machines, etc.
Although greater convenience has been attributed to the development of such electronic products, wastes thereof increase, thus generating serious environmental contamination.
Therefore, research on recycling the collected wastes is thoroughly under studying. In particular, with the intention of recycling Nd—Fe—B type magnet scraps, rare earth elements may be extracted therefrom, or the magnet scraps may be re-melted or converted to resin magnets.
However, an extracting process of rare earth elements from the Nd—Fe—B type magnet scraps suffers from being complicated, and requires high extracting costs. Further, a re-melting process is complicated, with recovery efficiency less than 50%, due to the high oxygen concentration of the magnets and oxidation during the recycling process. Thus, the above processes have no economic benefits, and most magnet scraps are buried.
Hence, since limitations are imposed on efficiencies of conventional recycling processes for magnet scraps, productivity and reliability are decreased.
Of commercially available magnetic powders, isotropic powders prepared by a melt spinning process as a rapid solidification process are suitable for use in the preparation of resin magnets. However, such isotropic powders have low magnetic characteristics and are expensive, and thus limited in application fields. Meanwhile, although the HDDR powders are anisotropic and thus have high magnetic characteristics, they are disadvantageous in terms of high preparation costs, and difficulty in the preparation on a large scale.